@steelbreeze/broker/lib/client.js

Lightweight publish and subscribe using Server-Sent Events for node and express

"use strict";
var __importStar = (this && this.__importStar) || function (mod) {
    if (mod && mod.__esModule) return mod;
    var result = {};
    if (mod != null) for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
    result["default"] = mod;
    return result;
};
Object.defineProperty(exports, "__esModule", { value: true });
var http = __importStar(require("http"));
var EventSource = require('eventsource');
/**
 * Returns the client API to the message broker, providing publish and subscribe operations.
 * @param config Configuration specifying the server, port and base URL path of the message broker server.
 * @returns Returns a client providing publish and subscribe operations.
 */
function client(config) {
    return {
        /**
         * Publishes a message to a message broker for other client to receive based on their subscriptions.
         * @param topicName The topic to publish on. This may be one or more URL segments.
         * @param data The data to publish on the topic
         * @param onError Optional error handler callback
         */
        publish: function (topicName, data, onError) {
            if (onError === void 0) { onError = undefined; }
            var post = http.request({ hostname: config.host, port: config.port, path: config.path + "/" + topicName, method: 'POST', headers: { 'Content-Type': 'text/plain', 'Content-Length': Buffer.byteLength(data) } });
            // trap and propigate error messages as required
            post.on('error', function (err) {
                if (onError) {
                    onError(err);
                }
            });
            // send message to the server
            post.write(data);
            post.end();
        },
        /**
         * Registers a subscription to messages on the given topic. The callback is called each time a message to published on the same topic.
         * @param topicName The topic to subscribe to. This may be one or more URL segments.
         * @param callback The function to call when data is publised on the topic; passing a message object.
         */
        subscribe: function (topicName, callback) {
            var eventSource = new EventSource("http://" + config.host + ":" + config.port + config.path + "/" + topicName);
            var lastEventId = -1;
            // process messages from the server
            eventSource.onmessage = function (event) {
                // perform a duplicate message check
                if (event.lastEventId !== lastEventId) {
                    lastEventId = event.lastEventId;
                    // propigate message to the client
                    if (callback) {
                        callback({ topicName: topicName, id: event.lastEventId, data: event.data });
                    }
                }
            };
        }
    };
}
exports.client = client;